The benefits of being able to effect such a variation when instigated according to engine speed and load etc., are torque increase, and emission reduction. Furthermore, fuel economy can be drammatically improved over the whole revolution range without power output penalties.
Variable valve timing has been proposed for some considerable time. However, the majority of the solutions proposed are quite complicated and usually require a twin-camshaft engine in order to be effective. The variable abilities rely upon the availability of separate camshafts for the inlet and exhaust valves. This means that by varying one (or both) shaft(s) relative to the other, an advance/retard situation can be realised thereby changing the overlap between the valve cycles and offering a wider "optimum" timing regime.